Ruling Corner - Random, (Most Likely) Unwritten Rules

#1. A card you control is a card on your side of the field. An effect you control is an effect you activated or applied, intentionally or not.

---

#2. You can never use cards your opponent controls to fulfill a cost or perform a summon unless a card explicitly mentions you can.

---

#3. Face-down cards do not have any verifiable properties beyond being "a monster" or "a spell or trap card."

Exceptions:

Tributing a monster for a cost, be it for a summon or a card like "Icarus Attack."

Performing the inherent special summoning method of a Fusion Monster using your own cards, such as "Chimeratech Fortress Dragon," "Gladiator Beast Gyzarus," or "Elemental Hero Air Neos." Note that this only extends to using your own cards, and as such your opponent's face-down machines cannot be used for "Chimeratech Fortress Dragon."

Performing a Fusion Summon. The method doesn't matter. Again, your opponent's face-down cards cannot be used for the likes of "Super Polymerization" if specific requirements need to be met for the Fusion Monster.

Performing a Ritual Summon.

As you can see, the tribute and fusion mechanics tend to be pretty lenient. Obviously, all these exceptions are void if the card in question asks you for face-up monsters.

---

#4. Unless they explicitly or implicitly say so themselves, or are ruled that way, monsters do not need to remain face-up on the field for their effects that have already been activated to resolve properly.

For example, "Mist Valley Soldier" explicitly states it must remain face-up for its effect to work. "Light and Darkness Dragon" implies it, since it needs to be able to alter its own stats. "Zombie Master" is ruled that way due to missing text in the TCG.

---

#5. Effects ALWAYS activate and resolve in the same place. There is no exception to this.

---

#6. Effects cannot be activated in the middle of a resolving chain. Mandatory effects will wait until the next possible opportunity to activate if their trigger was met in the middle of a resolving chain.